(a) Field of the Invention
This invention relates to an improved cathode assembly for the electrodeposition of metals, comprising a cathode having attached thereto a pair of non-conductive edge sticks. More particularly this invention relates to an improved cathode to which edge sticks may be more easily and permanently attached.
(b) Description of the Prior Art
In electrolytic metal refining and electrowinning processes it has long been realised that in order to be able to recover the deposited metal from the cathode "starter sheet" that often is used, it is necessary to protect the edges of the cathode. By this means, bridging of the deposited metal between the two faces of the cathode is prevented. Originally, wooden sticks were used, which had a groove adapted to fit tightly to the edge of the cathode. These wooden sticks suffer from many disadvantages, most of which arise as a consequence of the poor resistance of the wood to the generally very acid conditions obtaining in the electrolysis cells. Many attempts have been made to provide an edge stick which is both effective, and comparatively cheap, and at the same time both robust and capable of secure attachment to the cathode sheet. These two last desiderata have lately assumed more importance, since the use of cathode-stripping machinery has been introduced.
Most of the proposals made involve removal of material from the edge regions of the cathode in some way to provide a means of attachment for the edge strip. Thus in U.S. Pat. No. 684,291 (issued Oct. 8, 1901 to W. A. McCoy) is described a cathode with a grooved edge, the groove shape being unspecified, or with a perforated edge, to which asphalt is applied. In U.S. Pat. No. 1,470,883 (issued Oct. 16, 1923 to C. H. Schuh) is described a cathode having a rabbeted edge, which edge is perforated; a channel-like edge stick is used which is held on by rivets through the perforations. An improvement of this technique is described in U.S. Pat. No. 1,857,903 (issued May 10, 1932 to A. G. Wensley) wherein what may be described as rubber rivets are used. All of these proposals involve shaping the edge of the cathode before use.
Edge-shaping of the cathode can be an expensive procedure: various proposals have been made to avoid this and attach the edgestick by other means. In U.S. Pat. No. 1,994,144 (issued Mar. 12, 1935 to A. B. Merrill) a vulcanization procedure is proposed. Others have proposed to use adhesives. In U.S. Pat. No. 3,798,151 (issued Mar. 19, 1974 to A. Takamura et al) is proposed a wedge system, wherein a wedge is inserted into the outer face of the edge stick to cause it to bind more tightly onto the edge of an undeformed cathode. In U.S. Pat. No. 2,343,161 a related technique is proposed, involving a metallic channel-like stiffener inside a rubber channel edge stick. A further variant is described in U.S. Pat. No. 3,830,710 (issued Aug. 20, 1974 to J. S. Narozanski et al) wherein the edge of the cathode is notched at its upper and lower ends to retain an edge strip which is stretched to engage the cathode resiliently.
A very simple system involving split plastic tubing and a grooved cathode edge is described in U.S. Pat. No. 2,536,877 (issued Jan. 2, 1951 to W. A. Emmanuel et al) wherein the slit tubing is opened and the edge of the cathode inserted into the slit: in attempting to return to its circular configuration, the tubing engages into the grooves.
All of these systems suffer from either, or both, of two disadvantages: complexity and potential weakening of the cathode edges. And with complexity inevitably arises cost problems. Any edge weakening, as is caused, for example, by a continuous edge groove, is not desirable as this makes the assembly of cathode and edge sticks less robust, and thus less able to sustain the rigours of modern mechanical handling equipment, especially automated cathode stripping equipment.